The disclosure of Japanese Patent Application No. 2000-125661 filed on Apr. 26, 2000 is incorporated herein by reference in this entirety.
The present invention relates to a controller for a vehicle steering apparatus, and more particularly, to a controller of an electromotive power steering apparatus that generates auxiliary force used by a steering wheel to steer a vehicle, such as an automobile, with a motor.
In the prior art, an engine control system includes a main microcomputer (hereafter referred to as main computer) and a sub-microcomputer (hereafter referred to as sub-computer) to make the control system failproof. The outputs of the computers are compared. When the outputs differ, it is determined that the computation processing system has failed. The failproof technology is applied to a controller of an electromotive power steering apparatus, which includes a sub-computer and a main computer for monitoring the sub-computer. The sub-computer performs the same computations as the main computer in synchronism with the control cycle of the main computer. Then, the sub-computer compares the computation results of the main computer with its own computation results to determine whether the main computer has an abnormality.
To properly monitor the main computer, the sub-computer must perform computations in the same control cycle as the main computer. Thus, the sub-computer must have the same capability as the main computer. This increases the cost of the controller.
The employment of an inexpensive and low-capability sub-computer may decrease the cost of the controller. However, computations would not be synchronized with the main computer. Accordingly, the comparison of the computation results can be compared only once every predetermined number of main computer computations. This hinders accurate determination of the calculation result.
It is an object of the present invention to provide a controller of a vehicle steering apparatus that enables determination of computation results in the same control cycle as a main computer even when employing a sub-computer having a capability lower than that of the main computer.
The present invention provides a controller of a steering apparatus including a motor for generating auxiliary force applied to a steering wheel to steer a vehicle. The motor is controlled in accordance with an auxiliary torque command value. The controller includes a main computer for computing the auxiliary torque command value in a main control routine, which is repeated cyclically, based on steering torque generated by the steering wheel and velocity of the vehicle. A sub-computer computes a value equivalent to the auxiliary torque command value in a sub-control routine, which is repeated cyclically, based on the steering torque and the vehicle velocity. Each cycle of the sub-control routine is longer than each of the main control routine. A first comparison circuit compares the auxiliary torque command value with the steering torque in each cycle of the main control routine. A second comparison circuit compares the auxiliary torque command value and the equivalent value in each cycle of the sub-control routine.
In another perspective, the present invention is a method for detecting an abnormality in a controller of a steering apparatus including a motor for generating auxiliary force applied to a steering wheel to steer a vehicle. The controller includes a main computer and a sub-computer. The method includes computing an auxiliary torque command value of the motor with the main computer in a main control routine, which is repeated cyclically, cycle based on steering torque generated by the steering wheel and velocity of the vehicle. The auxiliary torque command value indicates the direction of the auxiliary force generated by the motor, and the steering torque indicates the steering direction of the steering wheel. The method also includes controlling the motor in accordance with the auxiliary torque command value, and computing a value equivalent to the auxiliary torque command value with the sub-computer in a sub-control routine, which is repeated cyclically, based on the steering torque and the vehicle velocity. Each cycle of the sub-control routine is longer than each of the main control routine. The method further includes comparing the direction of the auxiliary torque command value with the direction of the steering torque in each cycle of the main control routine, comparing the auxiliary torque command value and the equivalent value in each cycle of the sub-control routine, generating a first abnormality notification signal when the direction of the auxiliary torque command value and the direction of the steering torque do not match, and generating a second abnormality notification signal when the auxiliary torque command value and the equivalent value do not match.
Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.